Electrical power transformers, such as those used in facilities known as substations, use power at substantial voltages and currents, typically lowering the voltage drawn from long distance transmission lines and providing power to local distribution circuits and/or industrial customers. An electrical power transformer can support a power load which can be drawn from an area including said local distribution circuits and/or industrial customers, including for example factories, apartment buildings, housing developments, and the like, in turn located in the vicinity of the substations. Depending on the loads, electrical power transformers can be positioned to cover a power grid with comparable transformers used at power plants and other facilities to step up voltage to levels suitable for application to the long distance transmission lines.
Load current variations in power distribution systems affect voltage drops across both customer load impedances and distribution system elements. These voltage changes require compensating adjustments in transformer winding connections (“taps”) to maintain the available voltage at the loads within prescribed limits, with the intent of maintaining as close to a constant voltage as practicable at each distributed load. It is known in power distribution apparatus to include, with the requisite multi-tap power transformers, automatically controlled load tap changers (LTCs) that can adjust the voltage at which power is fed to large loads, typically several times per day but as often as hundreds of times per day. The tap changes can be made without interrupting the load current in some embodiments, hence the term “load tap changer.”
By physically moving its tap positions, a load tap changer (LTC) switches an energized transformer turn ratio to compensate for changes in voltages on the supply end of the transformer. Original LTC designs switched contacts were immersed in oil. The movement from tap to tap created an arc and these units were known as arcing in oil tap changers. Arcing in oil decreases oil quality and contact life cycle or duration. The use of vacuum interruption during switching began a few decades ago and its use is increasing with greater customer acceptance. However, these vacuum interruption devices do not have effective monitoring systems.
Accordingly, a monitoring system is needed to protect the equipment and system in the unlikely event of a bottle system failure.